Virtual Machine systems store entire state of virtual machines, including the configuration information, snapshots, the number of network adaptors including the networks they are attached to, and the contents of the virtual disks, e.g., the representation of data presented to the virtual machine in various virtual disk files. Typically the data portion of a virtual disk file is stored in a separate file than the virtual machine configuration information. Since most end users are usually interested in only the data and not, for example, the state information for the virtual machine, administrators regularly throw away configuration information file and preserve only the file that stores the virtual disk data.
When state information is lost an administrator has to recreate it; which today is re-creatable but is becoming increasingly frustrating as virtual machines start booting from devices that are not virtual hard disk (VHD) files and virtual firmware increasingly stores more state information. Accordingly, techniques for ensuring that configuration information for virtual machines is not lost are desirable.
Machines (virtual and physical) are moving toward using firmware that conforms to the Uniform Extensible Firmware Interface (UEFI) specification. UEFI compliant firmware includes additional information that is used to boot an operating system (such as the path to the boot loader) inside non-volatile random access memory (NVRAM). If a boot disk is moved to another machine, this information would need to be repopulated before the operating system could be booted. For example, in a physical environment, when physical machines boot from storage area networks (SANs) and operating systems on the SAN are cloned and booted on another physical machines this information is missing. Similarly, this problem is exacerbated in a virtual machine environment because administrators typically deploy a common image of an operating system to multiple virtual machines and move the virtual machines from one physical host to another. Accordingly, techniques for enhancing the boot process for migratable operating systems using firmware that stores information used in the boot process are desirable.